This example is both the first and the last optimization program written for an electronic circuit. It is far from perfect.

The temperature response of a CTN is exponential. It is thus nonlinear. In a battery charger application floating voltage varies linearly with temperature. A TL431 voltage reference sees its output voltage controlled by two resistors (r10, r12) and a thermistor (r11). The simulation is run at a given temperature. The thermistor is modeled in SPICE by a regular resistor. Its resistivity is assessed by the TCL script. It is set with a spice::alter command before running the simulation. This script uses an iterative optimization approach to try to converge to a set of two resistor values that minimizes the error between the expected floating voltage and the TL431 output.